I posed this question on Discord and got some varied responses.  I'd like to hear from everyone if possible, even the people that already said their piece on Discord.

I'm specifically looking for what your character thinks, if you yourself want to post your thoughts as well then by all means go for it.

I think this is such a clear-cut issue in that of course it is infidelity if done without the partner's knowledge or consent. Equally, it would not be infidelity if done with the partner's consent. If the partner is not okay with it, it's not okay.

So yes, this is infidelity.

Best,

Auctor Lucan

Sithick wouldn't understand the idea only later realizing 'wait holograms can do that?" and then book time in the holodeck.

Jack and Salem have probably both used holograms for sex in the past and so can't judge anyone for it.

In my opinion it's the equivalent of porn in their time. The important thing to realize is that a hologram can be programmed to respond anywhich way a person desires. They are not real, but a simulation, and the healthy mind would distinguish it. There are probably cases where people have gone too far and become obsessive but the same can be said for any adult actress or actor, some people can't distinguish when a person is faking it, and inevitably become over engrossed into the porn they consume.

It's important to remember that in a tng episode it was disclosed that legally what a person does on the holodeck can not be charged or held against them. I think this is very important to note that when Barkley is playing around with a virtual version of the crew he serves with one that actually likes him, and kisses a fake Diana there is legally no recourse for it.

Diana is a little unnerved as she should be, but the reality of the situation is that a base hologram has no rights, it's not real, and so if someone were to run a program that featured sexual violence they can't then be held accountable for what amounts to a rape fantasy even if you programmed in the body of a co-worker.

Looking at it from that context it seems that Holodeck porn is much the same as loading up a video with the tags 'forced', 'kidnapping', 'horror', etc. and probably not that uncommon.

That said porn addiction is a very real thing, and there is an episode on the orville that showcases how it could affect a persons relationship, it would definitely be a neat idea to explore further in an rp.

I'm with Lucan on this, doing it without knowledge or consent is absolutely cheating. There was that Episode of Voyager where Tuvok HAD to have sex with a  hologram due to Pon'farr and this issue came up. It wasn't something that Tuvok approved of by any means. Now for a more practical matter for an average pairing of people.... Yeah, still cheating. 

Though there could be some practical and educational uses for such a thing, sex ed, and other stuff, for those that are virginal, or haven't engaged in intercourse with another species. or hell, even to find out if it would feel good.  Not every species has the same configuration of genitals I'm sure. I mean, look, we know it works between Humans, Vulcans, and Klingons.... but as a practical matter, the geneital arrangement may be different. and I'd imagine that there would have to be a ahem, 'hands on' test to see if a particular individual may find such a thing pleasurable.

A relationship can absolutely happen, and be fulfilling without sex. But to know if an arrangement can work, or is pleasurable, I can absolutely see this being tried out for interspecies liasons. Hopefully discussed with partners beforehand. Some species may have spines, studs, teeth, growths, slime, etc. Andorians for example would probably be cold as fuck. (pun intended).

But it does boil down to, discussing things with a partner to try things out, in this case, to save the embarrassment of knowing that one party (or both) can't perform when the time is right.

It depends entirely on if the hologram is based on a sentient AI. 

If it's nonsentient, it's basically masturbating to pornography.  If it's a sentient AI, that's a thinking creature and therefore cheating.